Cell migration is intrinsic to cancer, wound healing, including both the promotion and inhibition of select cell populations to arrive at optimal outcomes (e.g., keloid formation where an exaggerated wound healing response results in excessive tissue formation), vasculogenic pathologies (e.g. diabetic retinopathy, age related macular degeneration, retinopathy of prematurity), inflammatory (e.g. migration of macrophages, neutrophils, eosinophils, basophils, lymphocytes and related cells) and normal and abnormal developmental processes.
Every year cancer claims the lives of hundreds of thousands of people worldwide. The populations of many of the heavily industrialized countries are particularly susceptible to cancer induced morbidity and mortality. In fact, cancer is the second leading cause of death in industrialized nations. For example, prostate cancer is the second most common malignancy in men. It is estimated that in 2002 in the United States nearly 180,000 men will be diagnosed with prostate cancer. Breast cancer is the most common female malignancy in most industrialized countries, and in the United States it is estimated that breast cancer will affect about 10% of women during their lives. Approximately 30 to 40% of women with operable breast cancer eventually develop metastases distant from the primary tumor.
Metastasis, the formation of secondary tumors in organs and tissues remote from the site of the primary tumor, is the main cause of treatment failure and death for cancer patients. Indeed, the distinguishing feature of malignant cells is their capacity to invade surrounding normal tissues and metastasize through the blood and lymphatic systems to distant organs. Cancer metastasis is a complex process by which certain cancer cells acquire substantial genetic mutations and perturbed signal cascades that allow them to leave the primary tumor mass and establish secondary tumors at distant sites. Metastatic cancer cells break adhesions with neighboring cells, dissolve the extracellular matrix, migrate and invade surrounding tissue, travel via the circulatory system, invade, survive and proliferate in new sites. Unfortunately, the molecular mechanisms that promote and restrain the metastatic spread of cancer cells have yet to be clearly identified.
Medical researchers have made considerable efforts to understand whether chemotactic agents are involved in metastasis and why particular cancers preferentially metastasize to certain sites. Breast cancer, for example, favors metastasizing to regional lymph nodes, bone marrow, and lung and liver tissues. Prostate cancer favors metastasizing to bone marrow. Several theories have been advanced to explain the preferential metastasis of certain cancers.
It has recently been shown that one important property of highly metastatic cells is their ability to respond to chemotactic agents such as paracrine and autocrine motility factors. For example, recent work done by Muller et al. provides evidence for chemotactic homing of breast cancer to metastatic sites. (Muller et al. “Involvement of chemokine receptors in breast cancer metastasis,” Nature, 410:50-56 [2001]); See also, M. More, “The role of chemoattraction in cancer metastases,” Bioessays, 23:674-676 [2001]). Muller et al. findings indicate that CXCR4 and CCR7 chemokine receptors are found on breast cancer cells and that ligands for these receptors are highly expressed at sites associated with preferential breast cancer metastases.
Previously described cell migration assays suffer from several problems. In particular, the assays are not standardized, lack sensitivity and reproducibility, and are not adaptable for conducting large numbers of assays in parallel.
What are needed are assay devices and systems for detecting and quantifying cell number and identifying their spatial location, wherein the systems are standardized and amenable to performing assays in parallel.